1. Field of the Invention
This invention relates mainly to a securing structure of a blade for a torque converter for use in industrial construction vehicles such as a fork lift truck etc., and especially to a securing structure and a method of securing a blade.
2. Description of the Invention
As illustrated in FIG. 9 and FIG. 10, a torque converter 100 for use in industrial construction vehicles generally has such a structure that plural metal blades 102 formed into annular shape (each one is shown in FIG. 9 and FIG. 10 respectively) are installed on a concave surface of a turbine shell 101, flanges 103 and 104 extending in opposite directions with each other along the circumference of the shell 101 are formed integrally and entirely on a convex periphery and a concave periphery of the blade 102, respectively. The flange 103 and 104 are tacked to the surface of the shell 101 and the outside surface of a core ring 105 by spot welding, respectively.
However, in such a structure, dispersion of installing distance and position of the blade 102 may occur because of the difficulty for locating the blade 102. The spot welding may also be impossible in some configurations of the blade 102, so that hand work must be employed. Thus, the manufacturing cost has been expensive. Moreover, the formation of these flanges 103 and 104 formed entirely on the convex and concave peripheries has increased the total weight of the whole torque converter. The formation would affect a flow of fluid (working oil).
Therefore, in recent years, a securing structure of blade to a torque converter 120 (only a turbine portion is shown) for use in a general passenger car has been adopted for industrial construction vehicles.
Such structure includes plural circular blades 122 which are secured to a concave surface of a shell 121 with some space in the circumferential direction. A core ring 123 is secured to a concave periphery of the blade 122 and extends along the circumferential direction of the shell 121. Slots 126 and 127 in which tabs 124 and 125 of the blade 122 are fitted are formed in the shell 121 and the core ring 123 respectively. An inlet portion X1 of the convex periphery of the blade 122 is tacked by brazing when a turbine wheel is assembled, and then the convex periphery of the blade 122 and concave periphery are brazed.
The structure has an advantageous feature in that positioning of each blade can be done easily when tacking by brazing. However, in the industrial construction vehicles such as fork lift trucks, special large loads must be required because changes of forward/backward shifting are carried out more frequently than in general vehicles such as a passenger car, and the turbine wheel may rotate in the reverse direction when the change of forward/backward shifting is carried out. It has been ascertained by experiments that, when the above-mentioned structure of the torque converter 120 is applied to this type of vehicle, a crack 130 as shown by FIG. 12 will be produced because of the excessive large torque load transmitted to the portion adjacent to an inlet of the blade 122. When the thickness of the blade 122 is increased in order to avoid the above trouble, a collision loss of fluid becomes large because a pressure area of the inlet of the blade 122 denoted by 131 increases (FIG. 13). The pressure area of the outlet of the blade 122 denoted by 132 also becomes large, so that eddies 133 (FIG. 14) may occur at the place adjacent to the fluid outlet end face 132 causing cavitation.
An object of the present invention is to solve the above-mentioned problems by employing ribs which extend in a circumferential direction of the shell and are only formed on both ends of the convex periphery and concave periphery of the blade, and by brazing the convex periphery and concave periphery to the shell and the core ring respectively.